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Building a Foundation
Angular Limb and Flexure Deformities in Foals
Stephen E. O'Grady, DVM, MRCVS
Angular limb and flexure deformities are
common limb abnormalities seen in foals that require early
recognition and treatment. Foals with angular limb deformities
have traditionally been referred to as "knock-kneed" or
"bow-legged" in the front limbs. Angular limb deformities can
also appear in the hind limbs but not as commonly. The
pathogenesis of this problem is not clearly understood but
suggested etiologies can be classified as either congenital
(present at birth) or acquired in the first few weeks of life.
The primary lesion is an imbalance of physeal growth; for
various reasons, growth proceeds faster on one side of the
growth plate than the other does. A valgus deformity is
defined as deviation of the limb away from the midline
(knock-kneed); a varus deformity is a deviation of the limb
toward the midline (bow-legged). The most common location of
angular limb deformity is the carpal joint (knee) where valgus
deformities are most often seen.
It is apparent that this knock-kneed conformation offers the
newborn a more comfortable stance while eating off the ground,
but most things are good in moderation and this deformity may
exceed acceptable limits. The deviation that exceeds 5-8
degrees becomes a concern. A few days of stall confinement on
firm bedding or limited exercise in a small paddock (one hour
twice a day) is a rewarding, cost-effective treatment for the
early valgus knee foal.
Radiographs (x-rays) should be part of the physical
examination in a foal with an angular limb deformity.
Occasionally severe abnormalities involving the bones of the
knee or at the level of the affected joint will preclude
correction of the problem. X-rays will also reveal the degree
of deviation, and allow comparison at a later date.
Conservative therapy for the management of most angular limb
deformities is successful in the newborn foal. This would
include squaring the toe of the hoof, restricting exercise and
occasional splinting. Restricted exercise would be either
strict stall confinement or brief periods of turnout in a
small area with firm footing for a half hour, two to three
times daily. This allows the growth plate to be stimulated but
prevents stress and compression on the affected side of the
growth plate. If the knee can be corrected by applying
pressure with one hand on the inside of the knee and counter
pressure with the other hand applied to the outside of the
fetlock, then a splint made from polyvinylchloride (PVC) pipe
fitted from the elbow to the fetlock can be applied for a few
hours daily. A full length bandage is applied to the limb,
then the PVC pipe is placed on the outside of the limb and
secured with a bandage which pulls the affected joint in that
direction. This is the most cost effective and many times the
most curative treatment available.
Acquired angular limb deformities can be graded from one to
four according to the degree of deviation. These can occur
anywhere from a few days onward. Grade one and two angular
limb deformities involving the knee will again respond to
restricted exercise and the use of an extension which is
applied to the inside of the foot. The extension on one side
and toward the back of the foot will support the overloaded
side of the limb, i.e. will move the plane of support toward
the midline to allow a more even distribution of weight over
the support surface. The extension also promotes centerline
breakover. The extension is made from a poly
methylmethacrylate (Equilox®) and fiberglass applied directly
to the foot and shaped to the desired width to provide the
exact amount of correction. It is trimmed like normal hoof as
the foot grows or additional applications can be applied as
deemed necessary. Again, splints would be optional depending
on the movement of the joint.
If grade three and four angular limb deformities do not
respond to conservative therapy (limited exercise, lateral
extensions, splints, etc.) they would undergo a surgical
procedure such as a periosteal elevation (PE). In severe
cases, this could be combined with a staple or screws and
wires on the opposite side of the joint if necessary. In many
cases, however, the surgical procedure is performed too early
before conservative therapy is allowed to correct the problem.
It has been shown that angular limb deformities involving the
knee will respond to surgery up to four months of age with
full correction. Recently, we have taken a different approach
to the surgery. Instead of periosteal elevation, we have been
removing a very small piece of bone (ulna) with very
encouraging results. This procedure can be done under local
anesthesia and leaves very little scarring.
Various deformities (bow-legged) involving the fetlock are
also very common in thoroughbred foals. This deformity can be
congenital or acquired. All acquired varus fetlocks occur
within the first few weeks of life. A varus fetlock deformity
requires early detection and treatment to correct due to early
closure of the growth plates of the fetlock. In the early
stages, the foal will have an inward arc to the limb in flight
when walked and will stand with the feet closer (to the
midline) than the fetlocks. Varus foals respond nicely to a
lateral extension (Equilox®) applied to the foot at ten days
of age and correction is usually completed at a month. If the
foal is presented for treatment after thirty days, then it
usually becomes a candidate for a periosteal elevation at the
fetlock. With both valgus and varus deformities, the earlier
corrective measures are instituted, the faster the problem
will resolve.
Flexure deformities have been traditionally referred to as
"contracted tendons." The primary defect is a shortening of
the musculo-tendonous unit rather than a shortening of just
the tendon portion, making "flexure deformity" the preferred
term. This produces a unit of functional length less than
necessary for normal limb alignment and leads to the clinical
signs of upright pasterns, prominent coronary bands and boxy
feet. If left untreated, it will lead to a condition where the
foal is unable to place the heel of his foot on the ground,
resulting in a typical clubfoot.
Flexure deformities present at birth are thought to be the
result of intrauterine positioning. These usually resolve in
the first few days of life with repeated intervals of brief
exercise in a small paddock.
Acquired flexure deformities are thought to be associated with
poor nutritional management in foals (increased protein,
unbalanced minerals, etc.). It is this writer's belief that
this syndrome is not part of the developmental orthopedic
disease (DOD) but a response to some form of pain. Any
discomfort in the foot or lower limb will initiate the flexion
withdrawal reflex which causes flexor muscle contraction and
altered position of a joint. I have seen this condition on
many farms where the feet were trimmed too short and excess
sole was removed from the foot, which causes marked toe
bruising. The first clinical sign one may see is abnormal wear
of the hoof wall at the toe. A closer look may reveal heat in
the feet, an increased pulse, pain on hoof testers, a
prominent coronary band and an upright pastern angle. This is
the time for conservative treatment: restricted exercise to
decrease continued trauma, the judicious use of
anti-inflammatory drugs to relieve pain, and the
administration of oxytetracycline which will cause muscle
relaxation, leading to normal foot-pastern alignment.
At the same time, Equilox® can be applied to the anterior hoof
wall to form a toe extension and the fiberglass continued over
the solar surface to protect that area from further bruising
(Fig. 3). This toe extension forms part of the foot and places
continuous tension on the muscular structures above the
tendon. If this condition is allowed to persist, it will
result in irreversible changes in the foot and joint capsule
requiring a surgical procedure for correction (check ligament
desmotomy).
A good working relationship between veterinarian and farrier
are necessary and important. A regular trimming program for
foals is essential and cost-effective when conducted as an
examination and maintenance exercise. Foals' feet should be
kept balanced, with adequate sole depth and maximum horn
length to protect the tender, vulnerable white line and
developing coffin bone.
Hoof care in the first four months of life is serious business
and should never be taken lightly. Discussion and management
with regard to feet and limbs during this period will dictate
the success of the foal as a sales yearling or mature athlete.
A sound foot care program is time consuming whereas
assembly-line trimming is easy, but the former is much more
beneficial. |
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